1. Field of the Invention
The present invention relates to a control device for a fuel cell vehicle using a fuel cell and an electric double layer capacitor, which are connected parallel to each other, as a power supply for a driving electric motor, and more particularly to a process of coping with the occurrence of an abnormal condition in the fuel cell.
2. Description of the Related Art
As a control device, mounted on a fuel cell vehicle, for controlling an output of a driving electric motor for the fuel cell vehicle, for example, a control device constituted as shown in FIG. 4 is known.
The control device shown in FIG. 4 has a motor driving unit 101 for supplying a driving electric energy to a driving electric motor 100 and a fuel cell 102 functioning as a power supply for an electric accessory such as an air-conditioner (not shown). An electric double layer capacitor 103 is connected parallel to the fuel cell 102. At the start time of the generation of an electric energy from the fuel cell 102, an electric energy is discharged from the electric double layer capacitor 103 to operate a reactive gas supply unit 104 which has an air compressor or the like and supplies reactive gases (hydrogen and air) to the fuel cell 102, so that the supply of the reactive gases to the fuel cell 102 is started.
An electric vehicle control unit 105 determines a target output (PD_REQ) of the electric motor 100 depending on a rotational speed (Nm) of the electric motor and the amount of depression (Ap) of an accelerator pedal.
A torque command determining unit 106, provided for the electric vehicle control unit 105, determines a torque command (TRQ_CMD) so that the electric motor 100 generates the target output (PD_REQ). A reactive-gas-supplied-amount determining unit 107, provided for the electric vehicle control unit 105, determines the supplied amount of reactive gases needed to achieve the target output (PD_REQ) and generates a signal indicative of a rotational speed (CMP_CMD) of an air compressor motor necessary to achieve the corresponding supplied amount of reactive gases. Consequently, the amount of generated electric energy depending on the target output (PD_REQ) can be obtained from the fuel cell 102, so that driving torque depending on the target output (PD_REQ) is generated from the electric motor 101.
However, in some cases, while the fuel cell vehicle is running, water which is produced by an electrochemical reaction of reactive gases remains in the fuel cell 102 to cause the occurrence of an abnormal condition in which the amount of electric energy generated by the fuel cell 102 decreases. While the target output (PD_REQ) is set at a high level as in the case of, for example, rapidly acceleration of the fuel cell vehicle, when the fuel cell 102 is in the abnormal condition and the amount of electric energy generated by the fuel cell 102 is lower than a level at which the electric energy necessary to operate the reactive gas supply unit 104 can be supplied, the electric energy discharged from the capacitor 103 is consumed by the motor driving unit 101 and the reactive gas supply unit 104, so that the electric energy charged into the capacitor 103 decreases abruptly.
As mentioned above, when the electric energy charged into the capacitor 103 decreases, there is the following disadvantage: It is difficult to keep the supply of the electric energy at a level necessary to drive the air compressor motor of the reactive gas supply unit 104. As a result, the fuel cell vehicle cannot run.
The present invention is made in order to solve the above disadvantage. It is an object of the present invention to provide a control device for a fuel cell vehicle, which suppresses such a fact that the fuel cell vehicle cannot run when an abnormal condition of a fuel cell is caused. There is provided a control device for a fuel cell vehicle, comprising: a fuel cell which is used as a power supply for a driving electric motor; an electric double layer capacitor, connected parallel to the fuel cell, for discharging for compensation for an insufficient electric energy when the amount of electric energy generated by the fuel cell is insufficient; reactive gas supply means, driven by an electric energy supplied from the fuel cell or the electric double layer capacitor, for supplying reactive gases to the fuel cell; and motor driving regenerative means, operated using the fuel cell and the electric double layer capacitor as a power supply, for regulating a driving electric energy supplied to the electric motor depending on a predetermined target torque to control driving torque generated in the electric motor and for regulating a regenerative electric energy recovered from the electric motor to the electric double layer capacitor to control regenerative torque generated in the electric motor.
The control device further comprises upper-limit-amount-of-generated-electric-energy recognizing means for recognizing the operating condition of the fuel cell to recognize the upper limit amount of electric energy generated by the fuel cell depending on the operating condition; current supply limiting means for limiting a current supplied from the fuel cell to the electric double layer capacitor and the motor driving regenerative means; capacitor-charging-amount-of-electric-energy recognizing means for recognizing the amount of electric energy charged into the electric double layer capacitor; and fuel cell abnormality countermeasure means for permitting the current supply limiting means to limit the current supplied from the fuel cell to the electric double layer capacitor and the motor driving regenerative means and permitting the reactive gas supply means to be driven by the regenerative electric energy of the electric motor when the upper limit amount of generated electric energy is equal to a predetermined amount of generated electric energy or lower and the amount of electric energy charged into the electric double layer capacitor is equal to a predetermined amount of charged electric energy or lower while the fuel cell vehicle is running.
According to the present invention, the fuel cell generates a current due to an electrochemical reaction of reactive gases. In some cases, water produced in association with the electrochemical reaction is not completely discharged from the fuel cell but the water remains in the fuel cell. The above-mentioned water remaining in the fuel cell interferes with the supply of the reactive gases to the fuel cell, resulting in a decrease in upper limit amount of electric energy generated by the fuel cell. The electric energy is discharged from the electric double layer capacitor for compensation for the insufficient amount of electric energy generated by the fuel cell, resulting in a decrease in amount of electric energy charged into the electric double layer capacitor. As a result, the fuel cell vehicle may not run.
While the fuel cell vehicle is running, when the upper limit amount of electric energy generated by the fuel cell is equal to the predetermined amount of generated electric energy or lower and the amount of electric energy generated by the fuel cell is equal to the predetermined amount of charged electric energy or lower, the fuel cell abnormality countermeasure means permits the current supply limiting means to limit the current supplied from the fuel cell to the electric double layer capacitor and the motor driving regenerative means and permits the reactive gas supply means to be driven by the regenerative electric energy of the electric motor.
As mentioned above, when the electric energy supplied from the fuel cell to the electric double layer capacitor and the motor driving regenerative means is limited, the amount of electric energy generated by the fuel cell decreases and the amount of reactive gases increases, the reactive gases being not consumed by the fuel cell but passing through the fuel cell as they are. Consequently, the discharge of water remaining in the fuel cell is advanced. The reactive gas supply means is operated by the regenerative electric energy generated in the electric motor produced by the running of the fuel cell vehicle, so that the advantages of advancing the discharge of water remaining in the fuel cell can be obtained continuously. Therefore, the recovery of the fuel cell to the normal condition is stimulated and such a fact that the fuel cell vehicle cannot run can be suppressed.
The fuel cell abnormality countermeasure means sets necessary regenerative torque as the target torque, the necessary regenerative torque being determined so that when the reactive gas supply means is driven by the regenerative electric energy of the electric motor, the amount of electric energy charged into the electric double layer capacitor is held at a level or higher, at which the electric double layer capacitor can supply an electric energy capable of operating the reactive gas supply means to the reactive gas supply means.
According to the present invention, when the fuel cell is not returned to the normal condition and the fuel cell vehicle stops running, the amount of electric energy charged into the electric double layer capacitor is held at the level at which the electric energy capable of operating the reactive gas supply means can be supplied to the reactive gas supply means. Accordingly, after the fuel cell is repaired or replaced with another one, the electric energy is supplied from the electric double layer capacitor to the reactive gas supply means to operate the reactive gas supply means, so that the generation of electric energy from the fuel cell can be started.
The control device further comprises speed detecting means for detecting a speed of the fuel cell vehicle. The fuel cell abnormality countermeasure means determines the necessary regenerative torque depending on the speed of the fuel cell vehicle.
According to the present invention, for example, when it is recognized on the basis of the speed detected by the speed detecting means that the fuel cell vehicle runs at high speed, the necessary regenerative torque is determined so as to prevent such a state that large regenerative torque is generated in the electric motor to abruptly brake the fuel cell vehicle. A change in motion of the fuel cell vehicle can be suppressed.